A138685 Numbers k such that there is no prime of the form 2k + p^2 for any prime p.

13, 28, 34, 43, 55, 58, 67, 73, 76, 88, 97, 100, 103, 106, 118, 133, 139, 145, 148, 157, 160, 163, 166, 178, 181, 184, 193, 199, 202, 208, 214, 223, 232, 238, 244, 253, 259, 262, 265, 268, 271, 283, 286, 298, 301, 307, 310, 313, 328, 331, 340, 343, 349, 352

Offset: 1

Author

Artur Jasinski, Mar 26 2008

Keywords

• nonn

Comments

Indices where zero occurs in A138479.

For primes in this sequences see A138686.

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A138479, A138686.

Programs

Mathematica

a = {}; Do[p = 0; While[(! PrimeQ[2*n + Prime[p + 1]^2]) && (p < 10000), p++ ]; If[p < 10000,[null], AppendTo[a, n]], {n, 1, 550}]; a
Select[Range[400],Mod[#,3]==1&&CompositeQ[2#+9]&] (* Harvey P. Dale, Feb 23 2017 *)

Formula

Based on comments from Zak Seidov, Don Reble and M. F. Hasler, we now know that these are the numbers k such that k == 1 (mod 3) and 2k + 9 is composite. - N. J. A. Sloane, Apr 20 2008